csci 127: introduction to computer science · yes, we will, since 1) it’s fundamental, and 2) the...

CSci 127: Introduction to Computer Science

hunter.cuny.edu/csci

CSci 127 (Hunter) Lecture 6 Summer 2020 1 / 35

Frequently Asked Questions

From previous semesters.

Could you spend more time on circuits/logical expressions/truth tables/decisions?We will start with that today, and more in the following weeks.

I still don’t get indices and the brackets. Could you spend more time on that?Yes, we will, since1) it’s fundamental, and2) the same ideas are used for accessing formatted data (today’s topic).

I still don’t get what is meant by input?Input is data provided to a program each time it runs, it may change at each run.In this course we have used the input() function.

Should I have received email for this course?Absolutely!!! We often send important communication by email. If you have notbeen receiving email from us weekly, please check your spam folder.

Could you spend more time on circuits/logical expressions/truth tables/decisions?

We will start with that today, and more in the following weeks.

I still don’t get indices and the brackets. Could you spend more time on that?

Yes, we will, since1) it’s fundamental, and2) the same ideas are used for accessing formatted data (today’s topic).

I still don’t get what is meant by input?

Input is data provided to a program each time it runs, it may change at each run.In this course we have used the input() function.

Should I have received email for this course?

Absolutely!!! We often send important communication by email. If you have notbeen receiving email from us weekly, please check your spam folder.

Today’s Topics

Recap: Logical Expressions & Circuits

Design: Cropping Images

Accessing Formatted Data

Design Challenge: Astrophysics andastropy

Today’s Topics

Recap: Logical Operators

in1 in2 returns:False and False False

False and True False

True and False False

True and True True

in1 in2 returns:False or False False

False or True True

True or False True

True or True True

in1 returns:not False True

not True False

True and True True

False or True True

True or False True

True or True True

not True False

True and True True

False or True True

True or False True

True or True True

not True False

Logical Operators & Circuits

Each logical operator (and, or, &not) can be used to join togetherexpressions.

Example: in1 and in2

Each logical operator (and, or, &not) has a corresponding logicalcircuit that can be used to jointogether inputs.

Examples: Logical Circuit

(in1 and in2) and in3

Examples: Logical Circuit

(in1 and in2) and in3

More Circuit Examples

Examples from last lecture:

Draw a circuit that corresponds to each logical expression:

not( in1 or in2 )

(in1 or in2) and (in1 or in3)

(not(in1 and not in2)) or (in1 and (in2 and in3))

Challenge Problem:

Predict what the code will do:

Python Tutor

(Demo with pythonTutor)

Today’s Topics

Challenge Problem: Design Question

From Final Exam, Fall 2017, V4, #6.

Design an algorithm that reads in an image and displays the lower leftcorner of the image.

Input:Output:Process: (Brainstorm for a “To Do” list to accomplish this.)

From Final Exam, Fall 2017, V4, #6.

Design an algorithm that reads in an image and displays the lower leftcorner of the image.

Input:Output:Process: (Brainstorm for a “To Do” list to accomplish this.)

Design Question

Design a program that asks the user for an image and then display theupper left quarter of the image. (First, design the pseudocode, and if time,expand to a Python program.)

How to approach this:

Create a “To Do” list of what your program has to accomplish.

Read through the problem, and break it into “To Do” items.

Don’t worry if you don’t know how to do all the items you write down.

Example:

1 Import libraries.2 Ask user for an image name.3 Read in image.4 Figure out size of image.5 Make a new image that’s half the height and half the width.6 Display the new image.

Design Question

Example:

Design Question

Example:

Design Question

Example:

Design Question

Example:

Design Question

Example:

1 Import libraries.

2 Ask user for an image name.3 Read in image.4 Figure out size of image.5 Make a new image that’s half the height and half the width.6 Display the new image.

Design Question

Example:

1 Import libraries.2 Ask user for an image name.

3 Read in image.4 Figure out size of image.5 Make a new image that’s half the height and half the width.6 Display the new image.

Design Question

Example:

1 Import libraries.2 Ask user for an image name.3 Read in image.

4 Figure out size of image.5 Make a new image that’s half the height and half the width.6 Display the new image.

Design Question

Example:

1 Import libraries.2 Ask user for an image name.3 Read in image.4 Figure out size of image.

5 Make a new image that’s half the height and half the width.6 Display the new image.

Design Question

Example:

1 Import libraries.2 Ask user for an image name.3 Read in image.4 Figure out size of image.5 Make a new image that’s half the height and half the width.

6 Display the new image.

Design Question

Example:

1 Import libraries.

import matplotlib.pyplot as plt

import numpy as np

2 Ask user for an image name.

inF = input(’Enter file name: ’)

3 Read in image.

img = plt.imread(inF) #Read in image from inF

4 Figure out size of image.

height = img.shape[0] #Get height

width = img.shape[1] #Get width

5 Make a new image that’s half the height and half the width.img2 = img[height//2:, :width//2] #Crop to lower left corner

plt.imshow(img2) #Load our new image into pyplot

plt.show() #Show the image (waits until closed to continue)

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

5 Make a new image that’s half the height and half the width.

img2 = img[height//2:, :width//2] #Crop to lower left corner

1 Import libraries.

import numpy as np

3 Read in image.

1 Import libraries.

import numpy as np

3 Read in image.

Today’s Topics

Structured Data

Common to have data structured in a spread sheet.

In the example above, we have the first line that says“Undergraduate”.

Next line has the titles for the columns.

Subsequent lines have a college and attributes about the college.

Python has several ways to read in such data.

We will use the popular Python Data Analysis Library (Pandas).

Structured Data

Open source and freely available (part of anaconda distribution).

Already loaded on the machines in 1001E North.

See end of Lab 6 for directions on downloading it to your homemachine.

To use, add to the top of your file:

import pandas as pd

Structured Data

import pandas as pd

Structured Data

import pandas as pd

Structured Data

import pandas as pd

Structured Data

import pandas as pd

CSV Files

Excel .xls files have much extra formatting.

The text file version is called CSV for comma separated values.

Each row is a line in the file.

Columns are separated by commas on each line.

CSV Files

nycHistPop.csv

Reading in CSV Files

To read in a CSV file: myVar = pd.read csv("myFile.csv")

Pandas has its own type, DataFrame, that is perfect for holding asheet of data.

Often abbreviated: df.

It also has Series, that is perfect for holding a row or column of data.

Example: Reading in CSV Files

nycHistPop.csv

In Lab 6

import pandas as pd

pop = pd.read csv(’nycHistPop.csv’,skiprows=5)

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

nycHistPop.csv

In Lab 6

import pandas as pd

pop.plot(x="Year")

plt.show()

Series in Pandas

Series can store a column or row of a DataFrame.

Example: pop["Manhattan"] is the Series corresponding to the column ofManhattan data.

Example:print("The largest number living in the Bronx is",

pop["Bronx"].max())

Series in Pandas

pop["Bronx"].max())

Series in Pandas

pop["Bronx"].max())

Challenge Problem

Predict what the following will do:

print("Queens:", pop["Queens"].min())

print("S I:", pop["Staten Island"].mean())

print("S I:", pop["Staten Island"].std())

pop.plot.bar(x="Year")

pop.plot.scatter(x="Brooklyn", y= "Total")

pop["Fraction"] = pop["Bronx"]/pop["Total"]

Challenge Problem

Solutions

Minimum value in the column with label “Queens”.

Average of values in the column “Staten Island”.

print("S I :", pop["Staten Island"].std())

Standard deviation of values in the column “StatenIsland”.

Bar chart with x-axis ”Year”.

Scatter plot of Brooklyn versus Total values.

New column with the fraction of population thatlives in the Bronx.

Solutions

Challenge Problem

cunyF2016.csv

Write a complete Python program thatreads in the file, cunyF2016.csv, andproduces a scatter plot of full-time ver-sus part-time enrollment.

Solution:

1 Include pandas & pyplot libraries.

2 Read in the CSV file.

3 Set up a scatter plot.

4 Display plot.

Challenge Problem

cunyF2016.csv

Solution:

4 Display plot.

Challenge Problem

cunyF2016.csv

Solution:

4 Display plot.

Challenge Problem

cunyF2016.csv

Solution:

4 Display plot.

Challenge Problem

cunyF2016.csv

Solution:

4 Display plot.

Challenge Problem

cunyF2016.csv

Solution:

4 Display plot.

Challenge Problem

cunyF2016.csv

Solution:

1 Include pandas & pyplot libraries.import matplotlib.pyplot as plt

import pandas as pd

2 Read in the CSV file.pop=pd.read csv(’cunyF2016.csv’,skiprows=1)

3 Set up a scatter plot.pop.plot.scatter(x="Full-time",y="Part-time")

4 Display plot.plt.show()

Challenge Problem

cunyF2016.csv

Solution:

import pandas as pd

Challenge Problem

cunyF2016.csv

Solution:

import pandas as pd

Challenge Problem

cunyF2016.csv

Solution:

import pandas as pd

pop=pd.read csv(’cunyF2016.csv’,skiprows=1)

Challenge Problem

cunyF2016.csv

Solution:

import pandas as pd

pop.plot.scatter(x="Full-time",y="Part-time")

Challenge Problem

cunyF2016.csv

Solution:

import pandas as pd

4 Display plot.

plt.show()

Challenge Problem

cunyF2016.csv

Solution:

import pandas as pd

groupby()

AustraliaRain.csv

Sometimes you have recurring valuesin a column and you want to examinethe data for a particular value.

For example, to find the average rain-fall at each location:

1 Import libraries.import pandas as pd

2 Read in the CSV file.rain =

pd.read csv(’AustraliaRain.csv’,skiprows=1)

3 Group the data by location averages.groupAvg =

rain.groupby(’Location’).mean()

4 Print the average rainfall at eachlocation.print(groupAvg[’Rainfall’])

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

Sometimes you have recurring values in a col-umn and you want to examine the data for aparticular value.

For example, to find the average rainfall atone location, e.g. Moree:

3 Group the data by location get averages forgroup Moree.MoreeAvg =

rain.groupby([’Location’]).get group(’Moree’).mean()

4 Print the average rainfall.print(MoreeAvg[’Rainfall’])

groupby()

AustraliaRain.csv

groupby()

AustraliaRain.csv

Today’s Topics

Design Challenge

On a piece of paper, design an algorithm that:

Prints the luminosity of the brightest star.

Prints the temperature in Kelvin (K) of the coldest star.

Prints the temperature in Fahrenheit of the coldest star. New:astropy.units will seamlessly convert!!!

Prints the average radius of a Hypergiant

Design Challenge - Solution

Libraries: pandas and astropy

Process:I Print max of ’Luminosity’ columnI Prints min of ’Temperature’ column and store it in temp variableI Use astropy to convert temp variable to Fahrenheit and printI groupby ’Star Type’ and take averages, then print max of ’Radius’

columnI OR groupby ’Star Type’ and get group ’Hypergiant’ to print

average ’Radius’

Process:I Print max of ’Luminosity’ column

I Prints min of ’Temperature’ column and store it in temp variableI Use astropy to convert temp variable to Fahrenheit and printI groupby ’Star Type’ and take averages, then print max of ’Radius’

Process:I Print max of ’Luminosity’ columnI Prints min of ’Temperature’ column and store it in temp variable

I Use astropy to convert temp variable to Fahrenheit and printI groupby ’Star Type’ and take averages, then print max of ’Radius’

Process:I Print max of ’Luminosity’ columnI Prints min of ’Temperature’ column and store it in temp variableI Use astropy to convert temp variable to Fahrenheit and print

I groupby ’Star Type’ and take averages, then print max of ’Radius’column

I OR groupby ’Star Type’ and get group ’Hypergiant’ to printaverage ’Radius’

column

I OR groupby ’Star Type’ and get group ’Hypergiant’ to printaverage ’Radius’

Design Challenge - Code

Libraries: pandas and astropyimport pandas as pd

import astropy.units as u

stars = pd.read csv(’Stars.csv’)

Process:I Print max of ’Luminosity’ column

print(stars[’Luminosity(L/Lo)’].max())I Prints min of ’Temperature’ column and store it in temp variable

minTempK = stars[’Temperature (K)’].min()

print(minTempK)I Use astropy to convert temp variable to Fahrenheit and print

KUnit = minTempK * u.K

print(KUnit.to(u.imperial.deg F, equivalencies = \u.temperature()))

I groupby ’Star Type’ and take averages, then print max of ’Radius’columnprint(stars.groupby([’Star type’])\.mean()[’Radius(R/Ro)’].max())

stars = pd.read csv(’Stars.csv’)Process:

I Print max of ’Luminosity’ columnprint(stars[’Luminosity(L/Lo)’].max())

I Prints min of ’Temperature’ column and store it in temp variableminTempK = stars[’Temperature (K)’].min()

print(minTempK)

I Use astropy to convert temp variable to Fahrenheit and printKUnit = minTempK * u.K

I groupby ’Star Type’ and take averages, then print max of ’Radius’column

print(stars.groupby([’Star type’])\.mean()[’Radius(R/Ro)’].max())

I OR groupby ’Star Type’ and get group ’Hypergiant’ to printaverage ’Radius’print(stars.groupby([’Star type’])\.get group(’Hypergiant’).mean()[’Radius(R/Ro)’])

Accessing Formatted Data:

I Pandas library has elegant solutions foraccessing & analyzing structured data.

I Can manipulate individual columns orrows (’Series’).

I Has useful functions for the entiresheet (’DataFrame’) such as plotting.

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csci 127: introduction to computer science · yes, we will, since 1) it’s fundamental, and 2) the...

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